Dry Drilling Of Aluminium Alloy Stack Materials

Abstract

The aerospace industry commissions the drilling of millions of holes annually on airframe structures. Unfortunately, as the drill moves through materials, cutting fluids tend to be released indiscriminately into the machining environment and workshop space. This creates health and safety challenges as workers breathe the airborne particles or are at risk of falling on slippery floors. The development of successful dry drilling processes will enable the aerospace industry to substantial improve the machining environment and address workplace health and safety concerns. Cutting fluids are used in machining and drilling to help reduce friction and heat, and flush out the resultant chips. The implementation of dry machining processes therefore requires a specific mechanism to manage potential issues brought about by eliminating cutting fluids. Several techniques have been implemented to address this situation; for instance the use of high quality cutting materials, modification of cutting tool geometries, optimising cutting parameters, and use of coatings. In this research, a range of coatings were studied to evaluate their machining effectiveness. This project was a collaboration between Kyocera Unimerco Ltd, Teer Coating Ltd, Airbus UK and the University of Manchester, UK. At the early stage of the research, experiments were conducted to examine the effects of cutting parameters using uncoated tools. Optimum cutting parameters were defined based on thrust force, hole quality, and tool wear conditions. Once ideal cutting parameters had been identified, assessments then continued towards evaluating most appropriate coatings in the machining of aluminium alloy stack materials. MoSTTM, doped MoS2, Graphit-iCTM, doped a-C, standard TiB2, modified TiB2, multilayer TiB2/doped MoS2, and CVD Diamond coated drills were evaluated in the study with uncoated carbide drills used as the benchmark. Results from the trial were then examined for the purpose of narrowing down the selection of coating to only four for the durability test. Simulation by Abaqus was conducted to calculate the minimum spacing required for the drilling of successive holes. The knowledge acquired on thermal affected zones made possible the application of Z-strategy to minimise thermal effects on the workpiece. Four coatings were selected for a durability test and evaluation of their effectiveness. Machinability was assessed in terms of hole diameter, surface roughness (Ra), thrust force, and torque. Successful baseline experiments employing these (1) four coatings, and (2) uncoated were conducted where it was later concluded that CVD diamond and hard DLC possessed the highest resistance to material adherence and minimum hole diameter. These were therefore recommended for the dry drilling of aluminium alloy 2024 and aluminium alloy 7150 stack. A separate test was performed with random coatings and cutting parameters for the purpose of assessing whether swapping material positions affected cutting performance. Results from the test indicated that drilling from aluminium alloy 7150 as top plate is a better option in terms of the surface roughness (Ra) of the workpiece. This research has provided evidence that the dry drilling of aluminium alloy stack materials could be successfully established with the use of appropriate coatings. The findings of this research are of very significant relevance and value to Teer Coatings Ltd as coating manufacturer, Kyocera Unimerco Ltd as tool supplier, and Airbus UK as the eventual end- user.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Carl Diver (Supervisor) & Paul Mativenga (Supervisor)